Exterior Angle Theorem

Introduction

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As a hook, ask students why understanding the exterior angle of triangles is important in real-life situations. Refer to the last page of the guided notes as well as the FAQs below for ideas.

Use the first page of the guided notes to introduce the concept of exterior angles of triangles. Walk through the definition of exterior angles and how they relate to the angles of a triangle. Emphasize the relationship between the exterior angle and the two remote interior angles. Refer to the FAQ below for a walk through on this, as well as ideas on how to respond to common student questions.

Continue with the second page of the guided notes to introduce the Exterior Angle Theorem. Teach students how to apply the theorem to find unknown exterior angles of triangles. Students will set up equations with Exterior Angle Theorem to solve for the missing variables. Highlight the significance of the theorem in solving geometric problems involving triangles.

Based on student responses, reteach concepts that students need extra help with. If your class has a wide range of proficiency levels, you can pull out students for reteaching, and have more advanced students begin work on the practice exercises.

Practice

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Have students practice solving problems involving exterior angles of triangles and the Exterior Angle Theorem using the practice worksheet (pg. 2), maze activity (pg. 3), color by number activity (pg. 4) provided in the guided notes resource. Walk around to answer student questions. You can also assign it as homework for independent practice.

Real-Life Application

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Use the last page of the guided notes resource to bring the class back together, and introduce the concept of how the Exterior Angle Theorem can be used in real life situations, such as in architecture and engineering when designing structures with angles, in navigation when determining directions and angles, or in art and design when creating geometric patterns and shapes. Students will read about some real life scenarios of how the Exterior Angle Theorem is used and then reflect on their reading with short sentences (pg. 5 of guided notes). Then, they will rate their mastery of the topic in a mini self assessment box on the bottom of the page.

Refer to the FAQ for more ideas on how to teach real-life applications of the Exterior Angle Theorem!

Additional Self-Checking Digital Practice

If you’re looking for digital practice for Exterior Angle Theorem, try my Pixel Art activities in Google Sheets. Every answer is automatically checked, and correct answers unlock parts of a mystery picture. It’s incredibly fun, and a powerful tool for differentiation.

Here’s 1 activity to explore:

• Exterior Angle Theorem Digital Pixel Art